CVS stands for Concurrent Versions Software and is an open-source package designed to allow multiple developers to work concurrently on a single source tree, recording changes and controlling versions. It is possible to cause a denial of service for users of CVS due to predictable temporary filenames. CVS uses locking directories in /tmp and combines the static string 'cvs-serv' with the process ID to use as filenames. This is trivial to guess for an attacker, and since /tmp is world writeable, directories can be created with predicted names. CVS drops root priviliges, so these directories cannot be overwritten and every session for which a locking directory has been already created (by the attacker) will be broken.